What you need to do is add empty .lproj folders for each language you support using the Copy Files section of the standalone builder. For French it would be fr.lproj and so on. This works for both OS X and iOS and will cause the system translate the standard dialogs like mail on iOS etc.

That's what I had already thought, but so far I didn't want to mess around with the LiveCode bundle.

Since to modify my final app bundle is not a valid option because of loosing the integrity of the signed bundle, I see two ways to go.
1. Have a look at the templates.
2. Make only apps with at least two languages and use the .lproj folders...

May be I should make an app to modify the templates via menus and drop downs.